Light is essential for plant growth, affecting plant morphology and physiology. Photovoltaic agriculture (APV) was proposed in the early 80s, but generating electricity on the farm field without influencing the growth of crops has been a challenge for researchers. In this paper, we proposed a newly designed improved photovoltaic agriculture system which can solve this problem optically. Using refraction from groove glass plates, the improved APV system provides crops appropriate light intensity and uniform illumination. We designed the groove glass plate by calculation and simulation. To investigate how different crop grows under different light environments, we examined yield and quality (nutrition) of lettuce under different light conditions. Four different treatments were applied including conventional field environment as the control, conventional APV facility, improved APV system and improved APV system with LED plant fill light lamps. The results indicate that lettuces under the improved APV system had similar yield to the control, and has more than twice the yield of lettuces under the conventional APV facility. In addition, lettuces grown under the improved APV system had a higher nutritional value. These results show that the improved APV system has advantages for wide spread application.
The measurement of plant growth’s light environment is the basis of urban agriculture, such as light-emitting diode plant factories. The photosynthetic photon flux density (PPFD) sensors, which measure the photon flux density of radiation in the spectral interval from 400 to 700 nm, cannot measure the spectral components, including the photon flux density of red light band and the photon flux density of blue light band, the light in these two bands are widely used in plant lighting. Facility agriculture, especially plant factories with artificial lighting, needs these data and their ratios by far, so a type of multichannel PPFD sensor is designed to solve these problems. First, we expound the design principle, circuit, and structure of the sensor, and calibrate the unregulated sensors by a standard PPFD sensor (PQS-1, Holland) under the calibration device constructed by controller based on DMX512 protocol. The test results show that the sensor’s average variance is 0.9956, which approximates the ideal linear response value 1. Meanwhile, we make a black opaque soft plastic anticrosslight sleeve using three-dimensional printing to solve the problem of crosslight on the sidewall of the filter, which let the crosslight error coefficient of the red and blue channels reduced by an order of magnitude and approached 0. Finally, we designed a set of light environment control systems, which can autocontrol the PPFD and light quality ratios, and a set of supplemental lighting systems, which can control the daily light integral, based on the sensors.